Adsorption mechanism study of multinuclear metal coordination cluster Zn5 for anionic dyes congo red and methyl orange: Experiment and molecular simulation

This study aimed to investigate the adsorption behaviors of congo red (CR) and methyl orange (MO) on the coordination cluster Zn 5 (H 2 L n ) 6 (NO 3 ) 4 (Zn 5 , H 3 L n  = 1,2-bis-(benzo[d]imidazol-2-yl)-ethenol). Due to multinuclear assembly, multinuclear Zn 5 possessed higher electrostatic potential and exhibited 3-fold enhancement in removal efficiency, compared with mononuclear Zn (Zn(H 3 L) 2 , H 4 L = 1,2-bis-(benzo[d]imidazol-2-yl)-1,2-ethanediol). The infrared and X-ray photoelectron spectroscopy and the electrostatic potential analysis indicated that the adsorption mechanism was electrostatic interaction and ion exchange interaction. The adsorption kinetics followed both the pseudo first-order and Bangham models. The pore system analysis and Bangham model suggested that CR and MO could diffuse in the snakelike pores of Zn 5 . The adsorption isotherms complied with the Langmuir isotherm model, and the maximum adsorption capacities for CR and MO are 166.91 and 100.78 mg/g at room temperature. The adsorption process was spontaneous and endothermic, driven by the entropy increase. Based on this research, the multinuclear coordination clusters can be suggested as potential adsorbents for the removal of anionic dyes.